
where \(\mu _1\) , \(\mu _2\) , and \(\kappa \)  are material properties.
They correspond—for consistency with linear elasticity in the range of small deformations—to the shear modulus \(\mu =\mu _1+\mu _2\)  and bulk modulus \(\kappa \)  of the material and are therefore related to the Young's modulus \(E\)  and the Poisson ratio \(\nu \)  via [1]}
\(\mu = \frac{E}{2\left(1+\nu \right)} \quad \mathrm {and} \quad \kappa = \frac{E}{3\left(1-2\nu \right)} \:.\) 
